@color: red;
.box (@border:yellow) {
  border: 2px solid @border;
}
#box2{
  width: 200px;
  height: 100px + 300px;
  background-color: @color;
  .op{
    width: 100px;
    height: 200px;
    background-color: rgb(158, 88, 88);
    .box(#000);
    span{
      color: blue;
    }
    &:hover{
      background-color: rgb(88, 152, 158);
    }
  }
}